Turbine blade rings and methods of assembly



Sept. 19, 1961 B. T. G. BISHOP TURBINE BLADE RINGS AND METHODS OF ASSEMBLY Filed April 18, 1960 IOA INVENTOR BHSIL T 6. BISHOP 3,000,612 TINE BLADE RINGS AND METHODS OF ASSEMBLY Basil Thomas George Bishop, London, England, assignor to D. Napier & Son Limited, London, England, a company of Great Britain Filed Apr. 18, 1960, Ser. No. 22,998 3 Claims. (Cl. 253-77) This invention relates to turbine blade rings, and this application is a continuation-in-part of my prior application Serial No. 636,729, filed January 28, 1957, now Patent No. 2,962,259.

A problem that is frequently encountered in turbines is that of blade vibration and various proposals have been made either for preventing vibration or for reducing its harmful effects. One such proposal has been to lace the blades together by means of a wire ring passing through holes in the aerofoil portions of all the blades. When the turbine rotor is rotating at high speed the centrifugal force acting on the unsupported sections of the wire between the blades presses the wire outwardly and may have the effect of bowing these unsupported sections outwardly between the blades. The wire therefore exerts frictional restraint against lateral flutter or transverse vibration of the blades, and is assisted in this by the said bowing out effect. One disadvantage of this arrangement is that the wire is disposed in the gas stream, which not only subjects the wire to high temperatures but may also interfere to some extent with the flow pattern of the gas stream passing through the blade channels.

It is an object of the invention to provide a turbine blade which utilizes wire lacing to counter transverse vibration of the blades, but in which the aforementioned disadvantage is avoided.

It is a further object to provide a form of wire lacing which does not require long lengths of wire.

These and other objects are fulfilled by a turbine blade ring according to the invention, a specific embodiment of which will be described herein in relation to the accompanying drawings, in which:

FIGURE 1 is a fragmentary view of a turbine blade ring embodying the invention; and

FIGURE 2 is a sectional developed plan view of the blade ring of FIGURE 1, on a larger scale.

In a turbine blade ring according to the present invention individual blades each comprising an aerofoil portion, a platform portion and a root portion are laced together by wire lacing passing through the platform portions, which lacing comprises several short lengths of wire each of which passes through holes in two adjacent platform portions and each blade being laced by at least one such wire to the adjacent blade on one side and by at least one other such wire to the adjacent blade on the other side.

Preferably, each end of each of the said short lengths of wire lies adjacent to an imperforate portion of the blade platform, which limits endwise movements of the short lengths of wire.

Assembly of the blade ring is facilitated if the short lengths of wire are disposed obliquely With their axes inclined to the circumferential direction.

An advantage of the invention is that the wire lacing is no longer located in the gas stream so that the aforementioned disadvantages are avoided. Moreover, assembly is facilitated as compared to an arrangement in which a single loop of lacing wire extends through the root portions of all the blades in the blade ring. Furthermore, the platform portion of each blade has at least two lacing wires passing through it.

The lacing has the effect of reducing blade vibration Patented Sept. '19, 1961 by restricting the transverse movements of the platform portion and hence of the blades as a whole.

Referring to the drawings, the turbine blade ring comprises a ring of turbine blades 10A etc. mounted around a turbine rotor disc 11. Each blade comprises an aerofoil portion 12, a platform portion '13 and a root portion 14. The platform portions 13 constitute a transition zone between the aerofoil portions 12 and the root portions 14, providing a smooth inner boundary to the blade channels which are defined between the aerofoil portions 12 of adjacent blades and at the same time providing a shield to prevent the hot gases which pass through these blade cannels from coming directly into contact with the highly stressed rotor disc 11. The platform portion consists of a transverse front wall 30, a transverse rear wall 31, and at least one web 26A etc. (FIGURE 2) extending from said front wall to said rear wall. Thus the platform portion is of approximately the shape of a letter I in cross-section, which provides adequate rigidity against torsional vibration. In order to prevent transverse vibration of the blades, holes are drilled in the webs 26A etc. platform portions13 and lacing wires-15 are threaded through these holes.

Referring to FIGURE 2, the web 26A, 26B etc. in the platform portion of each blade has two oblique holes drilled in it, the front hole in one web (e.g. 26A) being in alignment with the rear hole in the adjacent web 26B and so on. The blades are laced together with short lengths of wire. Thus the blade 10C is laced to the blade 10B by a short length of wire 15C which passes through the forward hole in the web 26B and through the rear hole-in the web 26C. The blade is also laced to the blade MD on its other side by a short length of wire 15D which passes through the front hole of the web 260 and through the rear hole of the web of the blade 10D. One end of the wire 15C lies adjacent an imperforate portion the web 26D whilst its other end lies adjacent an imperforate portion of the web 26A, whereby endwise movement of the wire is limited. Like considerations apply to all the other wires. Assembly is effected by holding the blades sufficiently far apart to permit the wires to be inserted, then bringing the blades close together in a jig into their final positions and moving the rotor disc endwise on to the root portions. This method of assembly is facilitated by the oblique disposition of the wires 15C, 15D etc.

The invention is applicable to axial flow compressors as well as to turbines, and accordingly the word turbine is used herein in a broad sense as embracing both turbines proper and axial flow compressors.

What I claim as my invention and desire to secure by Letters Patent is:

1. A turbine blade ring comprising a rotor, a ring of individual blades mounted on said rotor, each of said blades comprising an aerofoil portion, a root portion engaging said rotor, a platform portion intermediate between said aerofoil portion and said root portion, said platform portion having a transverse front wall, a transverse rear wall, and at least one web extending from said front wall to said rear wall, and wire lacing passing through said webs of said blades between said front and rear walls of said platform portions and having unsupported generally tangentially extending portions between adjacent webs to damp transverse vibrations of said blades, said wire lacing comprising a plurality of short rectilinear lengths of wire each of which passes through holes in said webs of at least two adjacent platform portions, and each of said blades being laced by at least one of said short lengths of wire to the adjacent blade on its one side and by at least one other of said short lengths of wire to the adjacent blade on its other side.

2. A turbine blade ring according to claim 1 in which each of said short lengths of wire has two ends and each of said ends lies adjacent to an imperforate part of a web of an adjacent platform portion, whereby said webs cooperate with the ends of the respective wire lengths to'limit their lengthwise movement.

3. A turbine blade ring according to claim 1 in which said short lengths of wire are disposed obliquely with their axes inclined to the plane of said blade ring.

UNITED STATES PATENTS Rydmark Apr. 20, 1943 Meyer May 16, 1944 Persson Sept. 8, 1953 Neumann Feb. 10, 1959 

